JP5367301B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte and a lithium secondary battery using the non-aqueous electrolyte.

The electrochemical element is an element utilizing an electrochemical reaction exemplified by a battery, a capacitor, an electrochromic element and the like.
Among these, lithium batteries are widely used as power sources for consumer electronic devices because of their high voltage and high energy density and high reliability such as storage stability. A typical example of the lithium battery is a lithium ion secondary battery. This includes a negative electrode using a carbon material capable of inserting and extracting lithium as an active material, a positive electrode using a composite oxide of lithium and a transition metal as an active material, and a non-aqueous electrolyte. It is a battery.

  Examples of the capacitor include an aluminum electrolytic capacitor and a non-aqueous electric double layer capacitor. Among these, the non-aqueous electric double layer capacitor includes a non-aqueous electrolyte between a positive electrode and a negative electrode using a high surface area electron conductive material such as activated carbon as an active material. Although it has a low energy density, it is characterized by high output, relatively high voltage, and long life. In the electric double layer capacitor, since electricity is stored by electrostatic adsorption of ions to the electric double layer on the electrode surface, a pure electrochemical reaction does not occur, but it is included in the electrochemical element discussed in the present invention in a broad sense.

  In recent years, electrochemical capacitors have been proposed as electrochemical elements having intermediate properties between lithium secondary batteries and capacitors. This is a capacitor configured to include, in an active material of at least one of a positive electrode and a negative electrode, a material capable of electrochemically inserting and extracting lithium and having a high surface area.

  Here, the non-aqueous electrolyte plays a role of transferring ions between the positive electrode and the negative electrode of the electrochemical element. In order to improve the charge / discharge characteristics of the electrochemical device, it is necessary to increase the ion transfer rate between the positive electrode and the negative electrode as much as possible. For this purpose, the ion conductivity of the non-aqueous electrolyte is increased, and the viscosity of the non-aqueous electrolyte is increased. It is necessary to lower the value. In addition, in order to enhance the life characteristics such as high-temperature storage characteristics and cycle stability of electrochemical devices, the non-aqueous electrolyte must be stable against positive and negative electrodes with high chemical and electrochemical reactivity. There is.

As a non-aqueous electrolyte satisfying such requirements, in lithium ion batteries, cyclic esters such as propylene carbonate, ethylene carbonate, and γ-butyrolactone, and chain forms such as diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, and methyl propionate are used. What melt | dissolved lithium salts, such as LiPF ₆ , in the mixed solvent with ester is mentioned. Moreover, in an electric double layer capacitor, what melt | dissolved electrolyte salts, such as tetrabutylammonium tetrafluoroborate, in cyclic esters, such as a propylene carbonate, ethylene carbonate, (gamma) -butyrolactone, is mentioned.

As an example of applying a phosphate ester to a non-aqueous electrolyte, a large amount of phosphate ester such as trimethyl phosphate, tri (trifluoroalkyl) phosphate, or triphenyl phosphate is mixed in an electrolyte solvent, Examples of flame retardant are given (for example, see Patent Documents 1 and 2).
By the way, with the recent remarkable improvement in functions of portable devices, there is a strong demand for electrochemical elements having a higher energy density than before. As a method for realizing such an electrochemical element, an electrode active material is filled in the electrochemical element at a higher filling rate.

  In this case, since the relative ratio of the electrolytic solution to the electrode is reduced, the alteration of the electrolytic solution is greatly related to the life characteristics of the electrochemical device. Moreover, in a lithium secondary battery, the method of raising the electric potential of the positive electrode of a full charge state rather than usual is illustrated (for example, refer patent document 4). When the potential of the positive electrode is increased, the amount of lithium occlusion / release per unit volume of the positive electrode can be increased as compared with the conventional lithium ion battery, and the battery voltage can be increased, so that the energy density of the battery can be improved. However, since the potential of the positive electrode at the time of full charge becomes high, the oxidative decomposition reaction of the electrolytic solution at the positive electrode is liable to occur, and the battery capacity can be reduced at a high temperature and the battery outer can swells due to the electrolytic oxidative decomposition gas. There is a risk that it is likely to occur.

From the above, in order to increase the energy density of the electrochemical element, it is important to suppress the decomposition reaction of the electrolytic solution. An example in which a small amount of phosphoric acid ester is added as an additive to suppress the electrochemical reaction of the electrolyte solution on the surface of the positive electrode or the negative electrode can be given (for example, Patent Document 3). However, no phosphoric acid ester has yet been found to exhibit satisfactory properties. Furthermore, there is still no example in which a predetermined phosphorus compound is applied to a lithium secondary battery.
Japanese Patent No. 3131905 Japanese Patent Laid-Open No. 3820495 Japanese Patent Publication No. 2006-221972 Japanese Patent Publication No. 2004-281158

  An object of the present invention is to provide a non-aqueous electrolyte solution that suppresses the oxidative decomposition reaction of the non-aqueous electrolyte solution on the electrode surface, particularly the positive electrode, and can suppress the deterioration of the life characteristics even in an electrochemical element with a high energy density. It is to be. Moreover, the subject of this invention is making the lithium secondary battery which uses the said non-aqueous electrolyte.

  In view of the above problems, the present inventors have intensively studied, and as a result, have completed the present invention. That is,

(1) A nonaqueous electrolytic solution containing 0.01 to 5% by weight of a compound represented by the following general formula (1) with respect to the whole nonaqueous electrolytic solution.

(In the general formula (1), A, -H, -OH, -OM (M represents a metal ion), a hydrocarbon group which may substituted or unsubstituted contain a hetero element having a carbon number of 1 to 12, or —NR ₂ (wherein R may be the same or different and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms) R ¹ and R ² are the same as each other; Or represents a substituted or unsubstituted hydrocarbon group which may contain hydrogen or a heteroelement having 1 to 12 carbon atoms.

  (2) The non-aqueous solution according to (1), wherein the compound represented by the general formula (1) includes at least one compound represented by the following general formulas (2) to (4): Electrolytic solution.

(In the general formulas (2) to (4), R may be the same or different from each other, and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms.)

  (3) The nonaqueous electrolytic solution according to (1) above, comprising a nonaqueous solvent containing a cyclic ester and / or a chain ester as a main component, and an electrolyte solute containing a lithium salt as a main component. It is.

  (4) At least a non-aqueous electrolyte solution according to any one of claims 1 to 3, a positive electrode having a positive electrode active material capable of reversible electrochemical reaction with lithium ions or anions, and lithium ion reversible. And a negative electrode having a negative electrode active material capable of electrochemical reaction.

  According to the nonaqueous electrolytic solution of the present invention, the oxidative decomposition reaction of the nonaqueous electrolytic solution on the electrode surface, particularly the positive electrode, can be suppressed. Therefore, when the nonaqueous electrolytic solution of the present invention is used, a high energy density electrochemical element, particularly a lithium secondary battery, in which the lifetime reduction due to the oxidative decomposition reaction of the electrolytic solution at the positive electrode is suppressed can be obtained. .

  Hereinafter, the present invention will be described in detail.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention contains a compound represented by the following general formula (1). The nonaqueous electrolytic solution of the present invention includes a compound represented by the following general formula (1), a nonaqueous solvent, an electrolyte solution, and other compounds as necessary. In addition, when the non-aqueous electrolyte of the present invention is used for a lithium ion secondary battery, a non-aqueous solvent containing a cyclic ester and / or a chain ester as a main component, an electrolyte solute containing a lithium salt as a main component, It is desirable to include.
However, in the nonaqueous electrolytic solution of the present invention, the compound represented by the general formula (1) is contained in an amount of 0.01 to 5% by weight based on the entire nonaqueous electrolytic solution.

  Here, the compound represented by General formula (1) is mix | blended in order to suppress the oxidative decomposition reaction of the non-aqueous electrolyte in the positive electrode in an electrochemical element (especially lithium secondary battery). When the compound represented by the general formula (1) is oxidized on the positive electrode, the biphenyl skeleton portion in the structure is oxidized and polymerized to form an oxide film, and then an insulating protective film is formed. Inhibits chemical oxidative degradation.

  On the other hand, it is known that condensed aromatic compounds such as biphenyl and terphenyl also form a film by oxidation polymerization at the positive electrode. However, the oxidative polymerization film formed with these compounds is a so-called conductive polymer, and is an electron conductive film, so that the electron transfer to the electrolyte solution through the film continues. The electrochemical oxidative decomposition reaction cannot be suppressed.

  On the other hand, the reason why the compound represented by the general formula (1) can form an insulating protective film is not clear, but the phosphate group bonded to the biphenyl skeleton changes the electronic state in the molecule, and the oxidized polymer. Is inferior in conductivity and is presumed to exhibit the effect of the present invention.

  Therefore, the nonaqueous electrolytic solution of the present invention suppresses the oxidative decomposition reaction of the nonaqueous electrolytic solution on the electrode surface, particularly on the positive electrode, and can suppress the deterioration of the life characteristics even in the case of an electrochemical element having a high energy density. When the nonaqueous electrolytic solution of the present invention is used, a high energy density electrochemical device, particularly a lithium secondary battery, in which the lifetime reduction due to the oxidative decomposition reaction of the electrolytic solution at the positive electrode is suppressed can be obtained. .

  In addition, the non-aqueous electrolyte of this invention is applied suitably for the electrochemical element using the electrochemical reaction illustrated by another battery, a capacitor, an electrochromic element etc. other than a lithium secondary battery.

  Hereinafter, each component will be described.

(Compound represented by the general formula (1))
First, the compound represented by the following general formula (1) will be described.

In the general formula (1), A, -H, -OH, -OM (M represents a metal ion), also may substituted or unsubstituted contain a hetero element having a carbon number of 1 to 12 hydrocarbon group, or - NR ₂ (wherein R may be the same as or different from each other, and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms) . R ¹ and R ² may be the same as or different from each other, and each represents hydrogen or a substituted or unsubstituted hydrocarbon group that may contain a heteroelement having 1 to 12 carbon atoms.

  Here, examples of M include alkali ions such as lithium ions, sodium ions, potassium ions, calcium ions, aluminum ions and magnesium ions, and transition metal ions such as copper ions, iron ions and nickel ions. Is done.

Examples of the hydrocarbon group that may contain a heteroelement having 1 to 12 carbon atoms include (1) aryl groups such as methyl group, ethyl group, vinyl group, allyl group, phenyl group, biphenyl group, phenylmethyl group, cumyl (2) Alkyloxy groups such as methoxy groups, ethoxy groups, vinyloxy groups, aryloxy groups, phenoxy groups, aryloxy groups such as biphenyloxy groups, phenylmethyloxy groups, etc. Oxygen-containing hydrocarbon groups such as aralkyloxy groups, (4) trimethylsilyl groups such as trimethylsilyl groups, triethylsilyl groups, alkylsilyl groups such as trivinylsilyl groups, alkyloxysilyl groups such as trimethoxysilyl groups, and trialkylsilyloxy groups Silyl-containing groups such as oxy groups, (5) methanesulfonyl , Trifluoromethanesulfonyl group, an alkylsulfonyl group such as a phenylsulfonyl group are exemplified. Moreover, the compound which substituted a part of hydrogen of the above-mentioned substituents with fluorine, such as a trifluoromethyl group, a trifluoroethyl group, a trifluoroethyloxy group, a fluorophenyl group, a pentafluorophenyl group, a fluorocumyl group, is also illustrated.
-NR ₂ includes (3) alkylamino groups such as dimethylamino group, diethylamino group and divinylamino group, arylamino groups such as diphenylamino group and di (biphenyl) amino group, and di (phenylmethyl) amino group. Examples thereof include nitrogen-containing hydrocarbon groups such as an aralkylamino group.

The hydrocarbon group which may contain a heteroelement having 1 to 12 carbon atoms may be substituted with a substituent represented by the following general formula (1-A). R ¹ and R ² in the following general formula (1-A) are the same as those in the general formula (1).

In the general formula (1), among the examples exemplified above, from the viewpoint of the formability of the insulating film on the positive electrode, which is the function of the present invention, R ¹ and R ² are hydrogen or have 1 to 1 carbon atoms. 6 is preferably a substituent having a small molecular volume, and most preferably hydrogen. A is preferably a hydrocarbon group, an oxygen-containing hydrocarbon group, or a nitrogen-containing hydrocarbon group from the viewpoint of not affecting the stability of the protective film of the negative electrode, and more preferably a carbon-carbon double bond. It is desirable to have.

  From the above viewpoint, the compound represented by the general formula (1) preferably has at least one structure represented by the general formulas (2) to (4).

  In general formulas (2) to (4), R may be the same as or different from each other, and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms.

  Here, in general formula (2)-(4), as a C1-C12 hydrocarbon group which R represents, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a heptyl group, an octyl group, Nonyl, decane, undeca, dodeca, vinyl, aryl, butenyl, pentenyl, peptenyl, octenyl, nonyl, decenyl, undecenyl, dodecenyl, ethynyl, propynyl, butynyl , Pentynyl group, peptinyl group, octynyl group, nonenyl group, decynyl group, undecynyl group, dodecynyl group, cycloheptyl group, cyclohexyl group, phenyl group, biphenyl group and other aryl groups, phenylmethyl group, cumyl group and other aralkyl groups, etc. And the like. Among the examples described above, from the viewpoint of suppressing the oxidative decomposition reaction, a methyl group, an ethyl group, a vinyl group, an aryl group, and a phenyl group are preferably exemplified. A vinyl group and an aryl group are more preferable.

  In the general formulas (2) to (4), it is particularly desirable that R represents hydrogen, a vinyl group, or an aryl group from the viewpoint of suppressing the oxidative decomposition reaction.

  Specific examples of the compound represented by the general formula (1) described above include the following compounds. However, it is not restricted to these specific examples.

  When the content of the compound represented by the general formula (1) is small in the non-aqueous electrolyte, the expression of action becomes insufficient, and when the content is too large, the ionic conductivity of the electrolyte decreases and the negative electrode resistance increases. May cause a decrease in battery output. Therefore, the content is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, and still more preferably 0.1 to 1% by weight with respect to the entire non-aqueous electrolyte.

(Non-aqueous solvent)
The non-aqueous solvent can be selected from known materials. In particular, in the case of an electrolyte solute for a lithium secondary battery, a cyclic ester and a chain ester are preferably exemplified, and the cyclic ester and / or the chain ester may be contained in the nonaqueous electrolytic solution as a main component. Here, the main component means containing 60% by weight or more based on the total amount of the electrolyte solute.

-Cyclic ester-
Examples of the cyclic ester include cyclic carbonates such as ethylene carbonate and propylene carbonate, and cyclic carboxylic acid esters such as γ-butyrolactone.
Cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, 1,2-pentene carbonate, 1,2-hexene carbonate, 1,2-heptene carbonate, 1,2-octene carbonate, 1,2-nonene carbonate 1,2-decene carbonate, 1,2-dodecene carbonate, 5,6-dodecene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,2-divinylethylene carbonate, 4-fluoroethylene carbonate, 4,5-difluoro Examples thereof include ethylene carbonate.
On the other hand, examples of cyclic carboxylic acid esters include lactones such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone, and alkyl lactones such as methyl γ-butyrolactone, ethyl γ-valerolactone, and ethyl δ-valerolactone. Examples are substitutions and the like.

  Among these, as the cyclic ester, ethylene carbonate, propylene carbonate, and γ-butyrolactone are desirable from the viewpoints of solubility of the electrolyte solute, solvent viscosity related to ionic conductivity in the nonaqueous electrolytic solution, and stability to the positive electrode and the negative electrode. . Moreover, since it has the effect | action which suppresses the reductive decomposition reaction of a negative electrode, vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, 4-fluoro ethylene carbonate, 4, 5- difluoro ethylene carbonate is 0.05 to 5 weight% Furthermore, it is desirable that an amount of 0.1 wt% to 2 wt% is contained with respect to the entire non-aqueous electrolyte.

-Chain ester-
Examples of the chain ester include chain carbonates such as dimethyl carbonate and diethyl carbonate, and chain carboxyl esters such as ethyl acetate and methyl propionate. As chain carbonates, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, dipentyl carbonate, dihexyl carbonate, dioctyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, methyl pentyl carbonate, methyl hexyl carbonate, methyl octyl carbonate , Ethyl propyl carbonate, ethyl butyl carbonate, ethyl pentyl carbonate, ethyl hexyl carbonate, ethyl octyl carbonate and the like. Further, as the chain carbonate, methyl-2,2,2-trifluoroethyl carbonate, ethyl-2,2,2-trifluoroethyl carbonate, fluoromethylmethyl carbonate, in which a part of hydrogen is substituted with fluorine, ( Examples also include difluoromethyl) methyl carbonate, ethyl fluoromethyl carbonate, and the like.
On the other hand, examples of chain carboxylic esters include carboxylic acid esters such as methyl acid, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

  Among these, as the chain ester, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate are preferable from the viewpoint of excellent ionic conductivity and viscosity of the electrolytic solution and improving the output characteristics of the battery.

-Mixing ratio of cyclic ester and chain ester-
The mixing ratio of the cyclic ester and the chain ester is represented by weight ratio, and the cyclic ester: chain ester is preferably 1: 99-80: 20, more preferably 5: 95-70: 30, and particularly preferably 10 : 90 to 60:40. By setting it as such a ratio, since the raise of the viscosity of electrolyte solution can be suppressed and the dissociation degree of electrolyte can be raised, the conductivity of the electrolyte solution regarding the charge / discharge characteristic of a battery can be raised.

  In addition, in order to improve the flash point of the solvent in order to improve the safety of the battery, as the non-aqueous solvent, a cyclic ester is used alone, or the mixed amount of the chain ester is changed to the whole non-aqueous solvent. It is desirable to limit the weight ratio to less than 20%. As the cyclic ester in this case, it is particularly preferable to use one or a mixture selected from ethylene carbonate, propylene carbonate, and γ-butyrolactone. Specific examples of the solvent combination include ethylene carbonate and propylene carbonate, ethylene carbonate and γ-butyrolactone, ethylene carbonate, propylene carbonate and γ-butyrolactone.

  When the chain ester is mixed in a weight ratio of less than 20% with respect to the total amount of the non-aqueous solvent, examples of the chain ester include a chain carbonate and a chain carboxylic acid ester. In particular, dimethyl carbonate, diethyl carbonate, diester Propyl carbonate, dibutyl carbonate, diheptyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, methyl heptyl carbonate and the like are desirable. In this case, the mixing ratio of the cyclic ester and the chain ester is preferably 80:20 to 99: 1, more preferably 90:10 to 99: 1, in terms of weight ratio.

-Electrolyte solute-
A known material can be selected as the electrolyte solute. In particular, in the case of an electrolyte solute for a lithium secondary battery, a lithium salt is preferably exemplified, and the lithium salt is preferably contained in the nonaqueous electrolytic solution as a main component. Here, the main component means containing 80% by weight or more based on the total amount of the electrolyte solute.

As the lithium salt, those commonly used in this field can be used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiN (SO ₂ C _k F _{( 2k + 1)} ) ₂ (k = 1 to 8 integer), LiPF _n (C _k F _{(2k + 1)} ) _(6-n) (n = 1 to 5, k = 1 to 8 integer), LiBF _n (C _k F _{(2k + 1)} ) _(4-n) (n = 1 to 3, k = 1 to 8). Moreover, the lithium salt shown by the following general formula can also be used. LiC (SO ₂ R ¹¹ ) (SO ₂ R ¹² ) (SO ₂ R ¹³ ), LiN (SO ₂ OR ¹⁴ ) (SO ₂ OR ¹⁵ ), LiN (SO ₂ R ¹⁶ ) (SO ₂ OR ¹⁷ ), LiN ( SO ₂ R ¹⁶ ) (SO ₂ F), LiN (SO ₂ F) ₂ (wherein R ^{11 to} R ¹⁷ may be the same as or different from each other, and are perfluoroalkyl having 1 to 8 carbon atoms) Group). Also, as borate ester lithium salt or phosphate ester lithium salt, bis (oxalato) lithium borate, difluoro (oxalato) lithium borate, bis (oxalato) fluorophosphate, trifluoro (oxalato) lithium phosphate Is mentioned. A lithium salt can be used individually by 1 type, or can use 2 or more types together.

Among these lithium salts, LiPF ₆ , LiBF ₄ , LiPF _n (C _k F _{(2k + 1)} ) _(6-n) (n = 1 to 5, k = 1 ₎ from the viewpoint of ion conductivity of the nonaqueous electrolytic solution. 8 _{integer), LiN (SO 2 CF 3} ) 2, LiN (SO 2 C 2 F 5) 2 is preferred.

  The concentration of the electrolyte solute in the nonaqueous electrolytic solution is usually 0.1 to 3 mol / liter. From the viewpoint of increasing the ionic conductivity and the viscosity of the electrolytic solution, it is desirable that the non-aqueous electrolytic solution contains 0.5 to 2 mol / liter.

[Other compounds]
The non-aqueous solvent according to the present invention may contain other compounds in the balance as long as the object of the present invention is not impaired. Other compounds include 1,3-propane sultone, 1,4-butane sultone, 1,3-prop-1-ene sultone, trimethyl phosphate, tris phosphate (2,2,2-trifluoroethyl), and phosphoric acid Examples include tris (trimethylsilyl), ethylene sulfate, propylene sulfate, butene sulfate, pentene sulfate, fluorobenzene, di (2,2,2-trifluoroethoxy) ethane, biphenyl, cyclohexylbenzene, toluene, and fluorotoluene.

  The addition amount of other compounds can be added within a range that does not impair the object of the present invention, and is exemplified by a total of 0.01 to 10% by weight with respect to the whole non-aqueous electrolyte. However, in the nonaqueous electrolytic solution of the present invention, if these additives are added excessively, the resistance of the battery is increased, and the charge / discharge cycle characteristics may be decreased. 01 to 2% by weight.

[Lithium secondary battery]
The lithium secondary battery of the present invention is capable of reversible electrochemical reaction with the non-aqueous electrolyte of the present invention, a positive electrode having a positive electrode active material capable of reversible electrochemical reaction with lithium ions or anions, and lithium ions. A negative electrode having a negative active material. By including the non-aqueous electrolyte of the present invention, that is, the lithium secondary battery of the present invention suppresses the oxidative decomposability of the electrolyte on the electrode surface, particularly the positive electrode. Even if the energy density of the chemical element is increased, the lifetime reduction can be suppressed.

  The lithium secondary battery of the present invention can take various known configurations as long as it takes these configurations, and is usually composed of a negative electrode, a positive electrode, and a separator, and is impregnated with the non-aqueous electrolyte of the present invention. It is a structure sealed in a metal can or a resin bag laminated with aluminum.

  The lithium secondary battery of the present invention can have any shape, for example, a cylindrical shape, a coin shape, a square shape, a film shape, or the like. However, the basic structure of the battery is the same regardless of the shape of the battery, and the design can be changed according to the purpose. For example, when the lithium secondary battery of the present invention is a cylindrical type, a wound body in which a sheet-like negative electrode and a sheet-like positive electrode are wound through a separator is impregnated with the non-aqueous electrolyte described above. The wound body is housed in a battery can so that the insulating plates are placed above and below the wound body. In the case of a coin type, a laminate of a disc-shaped negative electrode, a separator and a disc-shaped positive electrode is impregnated with a non-aqueous electrolyte, and if necessary, stored in a coin-type battery can with a spacer plate inserted. It becomes the composition which was done.

  The lithium secondary battery of this invention can be used for the same use as the conventional lithium secondary battery. For example, various consumer electronic devices, among others, mobile phones, mobiles, laptop personal computers, cameras, portable video recorders, portable CD players, portable MD players, electric tools, power sources for electric vehicles, It can be suitably used as a power source for household power storage.

  Hereinafter, main members will be described in detail.

(Positive electrode)
The positive electrode preferably includes a positive electrode active material layer and a positive electrode current collector.
As the positive electrode active material, any material that can electrochemically insert and desorb lithium or anions can be used without particular limitation. Examples of the substance capable of electrochemically inserting and removing lithium include lithium-containing transition metal oxides such as LiCoO ₂ and metal oxides not containing lithium such as MnO ₂ . Examples of substances that can electrochemically insert and desorb anions include carbon materials that can electrochemically dope and dedoped anions, and conductive polymers. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

  As the positive electrode current collector, known ones can be used. For example, Al, Ti, Zr, Hf, Nb, Ta, alloys containing these, and the like are formed on the surface by anodic oxidation in a nonaqueous electrolytic solution. Metal foils that form Usually, an electrode mixture obtained by mixing the above-mentioned positive electrode active material particles with a conductive agent such as acetylene black together with a binder such as polyvinylidene fluoride is pressed onto a metal foil of a positive electrode current collector and molded into a positive electrode sheet. use.

Here, in order to increase the storage density of lithium in the positive electrode unit volume, the positive electrode in a fully charged state may be charged to a voltage higher than 4.2 V with respect to the potential of metallic lithium. As such a positive electrode material, in addition to the conventional LiCoO ₂ , an oxide obtained by dissolving another transition metal in a spinel type Mn oxide as represented by the general formula of LiMn _x M _y O ₂ , LiNi Examples thereof include oxides in which Mn is partially dissolved in layered Ni or Co oxide to stabilize the structure, as represented by the general formula of _x Co _y Mn _(1-xy) O _2. .

(Negative electrode)
The negative electrode may include a negative electrode active material layer and a negative electrode current collector.
The negative electrode active material layer contains metallic lithium, a carbon material capable of occluding and releasing lithium ions, and a simple substance, compound, or any one of Al, Si, Sn, Sb, or Ge, and alloyed with lithium. Alloys that can be used as a negative electrode active material.

  The negative electrode active material layer is, for example, a mixture of negative electrode active material particles and a conductive agent with a binder such as polyvinylidene fluoride or SBR latex, which is molded on a metal foil such as a copper foil to form a sheet or film, Examples thereof include those in which active material particles are embedded in a metal sheet or on the surface to form a sheet or film, and those in which the negative electrode active material itself is formed into a thin film.

(Separator)
The separator is a film that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and a porous film, a nonwoven fabric film, a polymer electrolyte film, or the like can be used. The porous film is preferably a microporous polymer film, and the material thereof is polyolefin, polyimide, polyvinylidene fluoride, polyester or the like. A porous polyolefin film is particularly preferable, and specific examples thereof include a porous polyethylene film, a porous polypropylene film, and a multilayer film of a porous polyethylene film and polypropylene. The porous polyolefin film may be coated with another resin having excellent thermal stability and chemical stability such as PVDF.

  Examples of the polymer electrolyte membrane include a polymer in which a lithium salt is dissolved, a gel polymer electrolyte using a non-aqueous electrolyte as a plasticizer, and the like. The nonaqueous electrolytic solution of the present invention can also be used as a plasticizer for a polymer electrolyte.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited by this Example.

[Examples and Comparative Examples]
Non-aqueous electrolytes for each test were prepared as follows, and non-aqueous electrolytes of Examples and Comparative Examples were obtained.

-Preparation of non-aqueous electrolyte-
Ethylene carbonate (abbreviation EC) is used as the cyclic carbonate, diethyl carbonate (DEC) is used as the chain ester, EC and DEC are mixed at a weight ratio of 4: 6, and a nonaqueous solvent is prepared. ₆ (electrolyte solute) was prepared so as to have a concentration of 1 mol / l, and further 1 wt% of vinylene carbonate was used as a base electrolyte. To this base electrolytic solution, 0.2 wt% of the compound represented by the general formula (1) or the comparative compound was blended as an additive to prepare a test electrolytic solution.

[Evaluation of inhibitory effect of oxidative degradation by CV measurement]
CV (cyclic voltammogram) measurement was performed in order to evaluate the inhibitory effect on the oxidative degradation of the nonaqueous electrolytic solution for test. A glass cell with a heat insulation jacket was charged with 5 ml of an electrolyte, and a reference electrode, a counter electrode, and a working electrode were inserted into the glass cell and sealed to obtain a measurement system. In order to prevent moisture and oxygen from entering the measurement system, the measurement was performed in a glove box equipped with a gas circulation purification device.

  Here, metallic lithium was used for the reference electrode and the counter electrode, a glassy carbon electrode having an electrode area of 2 mmφ was used for the working electrode, and the measurement temperature was 60 ° C. In order to investigate the behavior on the oxidation side, the voltage change cycle in which the potential of the working electrode is increased from 3 V to 5 V at a rate of 10 mV / second and then returned to 3 V at the same rate with respect to the reference electrode lithium as one cycle. Two cycles were performed, and the oxidative decomposition current of the electrolyte flowing at this time was measured.

Then, as an index for the degree of inhibition of oxidative decomposition of the non-aqueous electrolyte at the positive electrode, the degree of inhibition of oxidative electrolysis shown in the following formula was obtained, the respective electrolytes were compared, and the results are shown in Table 1 and Table 2. It was.
Expression: Oxidation electrolysis inhibition level = [decomposition current at 4.9 V in the second cycle] ÷ [decomposition current at 4.9 V in the first cycle]

From the above results, it can be seen that the nonaqueous electrolytic solution of the present invention is excellent in the degree of inhibition of oxidative electrolysis.
Therefore, it can be seen that when the non-aqueous electrolyte of the present invention is used, a high energy density electrochemical element, particularly a lithium secondary battery, in which the lifetime reduction due to the oxidative decomposition reaction of the electrolyte at the positive electrode is suppressed can be obtained. .

Claims (4)

A nonaqueous electrolytic solution comprising a compound represented by the following general formula (1) in an amount of 0.01 to 5% by weight based on the whole nonaqueous electrolytic solution.

(In the general formula (1), A, -H, -OH, -OM (M represents a metal ion), a hydrocarbon group which may substituted or unsubstituted contain a hetero element having a carbon number of 1 to 12, or —NR ₂ (wherein R may be the same or different and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms) R ¹ and R ² are the same as each other; Or represents a substituted or unsubstituted hydrocarbon group which may contain hydrogen or a heteroelement having 1 to 12 carbon atoms. The non-aqueous electrolyte according to claim 1, wherein the compound represented by the general formula (1) includes at least one compound represented by the following general formulas (2) to (4).

(In the general formulas (2) to (4), R may be the same or different from each other, and represents hydrogen or a hydrocarbon group having 1 to 12 carbon atoms.)   The nonaqueous electrolytic solution according to claim 1, comprising: a nonaqueous solvent mainly comprising a cyclic ester and / or a chain ester; and an electrolyte solute mainly comprising a lithium salt. at least,
A nonaqueous electrolyte solution according to any one of claims 1 to 3, a positive electrode having a positive electrode active material capable of reversible electrochemical reaction with lithium ions or anions, and reversible electrochemical reaction with lithium ions And a negative electrode having a negative electrode active material.